Line scan device utilizing cavitation phenomena produced in an ultrasonic cell



TJJ VLJLLI Frpslob HU LJ) CA xR 3,305,977 K g W ...H Feb Y. 3,306,977 AUEHOMEINA M" "PROUCEU 1N AN ULTKASONIU Gmbh' Filed Dec. 6, 1963 2 Sheets-Sheet 1 gig l @www ATTORNEY Feb. Z8, 1967 H. P. BRUEGGEMANN 3,306,977 LINE SCAN DEVXCE UTILZNU CAVITATION PHENOMENA PRODUCED IN AN ULTRASONIC CELL Filed Dec. 6. 1963 2 Sheets-Sheet 2 HARRY P. BRUEGGEMANN ATTORNEY 3,306,977 Patented Feb. 28, 1967 3,306,977 LINE SCAN DEVICE U'I`ILIZING CAVITATlOt` PHENOMINA PRODUCED IN AN ULTRA- SONIC CELL Harry P. Brueggemann. San Marino. Calif., asslgnor to The Marquardt Corporation, Van Nuys, Calif., a corporation of California Filed Dec. 6, 1963. Ser. No. 328,708 7 Claims. (Cl. 178-7.6)

This invention relates to apparatus for electro-optical scanning, and more particularly to radiant energy scanning apparatus in which cavitation phenomena produced in an ultrasonic cell are used to horizontally scan an obiect or scene in order to couvert thcimage thu-s scanned directly into a video signal.

Various video pickup devices have been constructed heretofore for translating an image into a corresponding electrical (video) signal. High-resolution video display devices and wide-band video amplifiers for use with conventional video pickup devices are within the state-of-thcart. However. conventional video pickup devices such as image orthicon or vidicon tribes are limited in resolution which is typically of the order of 800 lines and is, therefore, inferior to the remaining links in the video transmission system. as regards resolution. The limit of pictorial excellence is, in part, established by scanning standards which define the number of lines into which the image is dissected in the scanning process. The number of lines must be sufiicient to providea fine enough image structure to satisfy the eye under normal viewing conditions. Values of 405, 525, 625. and 819 lines per picture are standardized in various countries. The standard in North America is 525 lines. This number is the total of all the lateral traverses in the scanning pattern from the beginning of one image frame to the beginning of the next image frame. The horizontal resolution generally exceeds the vertical resolution and may be defined in terms of lines even though the traverse is continuous rather than discrete lines as in the vertical scan. The horizontal scanning direction, standardized throughout the world, is from left to right along each line. and the vertical direction is from the top of the image to the bottom of the image.

There is provided by the present invention a highresolution video pickup device which is fully compatible with the resolution and bandwidth capabilities of the rcmaining elements in a video transmisison system. For example, in a typical construction, a resolution of 2400 lines may be achieved.

The apparatus of the present invention employs an electro-optical image dissector or line-scaning device which utilizes the principle of cavitation induced in a liquid by ultrasonic sound waves to .control tbc diffraction of a light beam passing therethrough. In a typical construction the apparatus of the invention comprises a transparent. liquid-filled cell, which is ultrasonically excited for horizontally scanning a line clement of an image and a photomultiplier tube responsive to the light output from the cell to produce an output video signal of high resolution. The cell or line-scan portion of the device essentially comprises a transparent liquid-filled cell in which hydrodynamic cavitation can be induced in order to establish a sweeping wave pattern of bubbles in the liquid. That is, vertical lines of extremely small bubbles are formed by the cavitation and produce a diffraction grating effect on light rays striking them at the plane or synunctry of the cell. A suitable ancillary optical system is used to image the scene of interest onto the cell. As these vertical lines of bubbles move across the cell in a sweeping motion, the incoming light rays are dilfractcd in a corresponding sweeping fashion upon interception by the lines of bubbles. Diffracted and untlifi'racted rays leaving the cell are directed to a Schlieren optical system which blocks the undiffracted rays and allows only the ditl'raeted rays to pass. The diffracted rays arc then focused by suitable optical elements onto a photomultiplicr tube.

If the light rays passing through the lilies of bubbles in the cell comprise a line portion of an optical image focused by the ancillary input optics, the bubbles will then sample a portion of this optical image. Output of light diffracted into the photomultiplicr tube is a function only of the amount of light received from the optical image at the location of the lines of bubbles. As a result the optical image is horizontally scanned and thc output from the photomultiplier tube is then a video signal derived from the line scan of the optical image. This video signal is identical to the video signal produced by a conventional video pickup tube, with the exception that the signal thus produced has a considerably higher resolution and a lower noise level than video signals derived from either a conventional vidicon or an image orthicon tube.

The photonmltiplier tube used to detect the dilracted light from the cell is an inherently low-noise level device because thermal noise is nearly absent. with only shot noise present. The conventional image orthicon tube uses a pholomultiplicr type of current amplifier, however, it amplilics the current from a noisy scanning beam. ln the present invention, however. the photomultiplicr amplilics the current from a photocmitting surface, which is much lower in noise content than the conventional scanning beam of the image orthicon. The inherent simplicity of the apparatus of thc invention, as compared with conventional video pickup devices is a distinct advantage in addition to the improved resolution attainable therefrom.

lt is therefore a principal object of the invention to provide novel and improved means for scanning an image or a scene and providing a corresponding video output signal.

Another object of the invention is to provide novel and improved means for image dissection.

An object of the invention is to provide novel and improved means for electro-optical scanning, corresponding to the horizontal output from a conventional television camera.

Still another object of the invention is to provide novel and improved ultrasonic light cell scanning apparatus.

Yet another object of the invention is to provide light scanning apparatus employing cavitation phenomena to control diffraction of light into a photoelectric transducer.

It is another object of the invention to provide novel and improved radiant energy scanning means which employs a plurality of lines of microscopic bubbles to cause diffraction of the radiant energy passing therethrough.

Another object of the invention is to provide improved video pickup apparatus having higher resolution than obtainable from prior video pickup devices.

Still another object of the invention is to provide video pickup means employing ultrasonic energy to dissect an image.

Another object of the invention is the improvement of video scanning apparatus. generally.

A general object of the invention is to provide novel and improved radiant energy scanning apparatus which overcomes disadvantages of previous means and methods heretofore intended to accomplish generally similar purposes.

Many other advantages. features and additional objects of the line scan device of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment. incorporating the principles of the present invention is shown by way of the illustrative example. In the drawings:

FIGURE 1 is a blocdiagram. incorporating a somewhat diagrammatic perspective view of the ultrasonic light cell and ancillary optical portion of the apparatus, of a line scan system for generating a high-resolution video output signal.

FIGURE 2 is a somewhat diagrammatic perspective view of the ultrasonic light cellportion of the scanning apparatus of the invention.

As stated hereinabove the invention is. in escnce. a device for scanning a lin'c element of an optically focused image, and producing an output video signal of highresolution therefrom. In a preferred embodiment, the line element comprises a horizontal line of an image to be televised. Vertical scanning of an image to be televised in accordance with conventional television standards occurs at a substantially lower frequency than docs horizontal scanning and is, therefore, not as susceptible to image degradation. For this reason, it is contemplated that conventional means may be used to vertically scan the image to provide the horizontal line input to the device described hereinafter as a preferred embodiment. However. the apparatus of the invention is not necessarily so limited. and both horizontal and vertical image dissection maybe achieved by means of the method and apparatus of invention. as will appear.

FIGURE 1 shows a typical system incorporating an ultrasonic light cell modulator according to the invention to provide the horizontal line scan function of a video pickup (television camera) system. As cart bc .seen in FIGURE l, light from the object l to be scanned is eollectcd by objective lens 2 and is transmitted to the vertical sweep equipment 3. which can be of the rotatingmirror type, or a vertical sweep device such as that dcscribed in copending appl"ation Serial No. 339.521 filed January 2l, i964, and of common assignee herewith. The function of the vertical sweep equipment 3 is to move the optical image, formed by lens 2 in the plane of symmetry of the ultrasonic cell 4. verticallyl downward. The centerline of the optical system is indicated at 5. and the plane of symmetry of cell 4 is normal thereto, and is indicated at 6 in FIGURE 2. Any means suitable for downwardly shifting the image focused at the plane of symmetry 6 may be employed for the vertical sweep equipment 3. This vertical sweep must be done without the image being deviated from the plane of symmetry and within the region of the ultrasonic cell windows 7 and 8. The rate of the vertical sweep preferably conforms to that commonly used in conventional television systems such as 30 frames pcr second in North America, or 25 frames per second in Europe.

The ultrasonic light cell 4, receiving the image from the vertical sweep equipment 3, consists essentially of a liquid enclosing container 9 with front and rear transparent windows 7 and 8 as shown in FIGURE 2. With further reference to FIGURE 2. there is sealed within the container 9 a suitable fluid such as water` in which hydrodynamic cavitation can be induced under suitable conditions of imposed high-frequency acoustic energy. 0n each end ofthe container 9 is an array of electro-acoustic transducers, each of which is so arranged as to focus generated ultrasonic wave trains through the water by Frcsnel diffraction. and across the cell in opposing directions, within a thin vertical plane previously designated as the plane of symmetry 6. Each transducer may comprise an array of piezoelectric crystals disposed at cach end of container 9. The rst array comprises crystals ll-lS which are excited in parallel via line 16, and concentrate the ultrasonic energy along the plane of .symmetry 6. In addition to concentrating the acoustic energy in a plane. the array of crystals (ll-l5) can be designed to concentrate the energy so as to compensate for losses of absorption by the liquid as the acoustical energy is propagated through the from array cell liquid. Also. the array may be arranged to rapidly diffuse the energy at the end of the scan cycle so that together with the absorption ofthe remaining energy by the end walls of the container 9. only a very`small amount of energy will be reflected back into the cell. The second array is similar to the first array and comprises crystals 17-21 which are excited in parallel via line 23.

While the crystal arrays shown h. vc five elements each. `the invention need not be so limited. Three elements are considered to constitute the simplest practical array ca- ;pable of concentrating and focusing the energy. The number and arrangement of the crystals in an array can be determined from the physical parameters of the cell using Cornu's spiral. or Frcsnefs-intcgrals in a manner well known to those skilled in thc art.

Continuous excitation at ultrasonic frequency is applied to the first array (ll-l5) via line 16. The second array (E7-23) is c vclically or intermittently excited with bursts at ultrasonic frequency. The sources of thcc eX- citation signals will now be described.

Referring again to the system illustrated in FIGURE l. a pulse from the sync pulse generator 2-9- is fed to the modulator Z5 via liuc` 26. which allows a 2t) mcgacycle (nrc.) wave burst to pass from the 2() mcgacyclc oscillator 27 via line 23 to the sync pulse amplifier 29 via line 3ll. The output from the` sync puh-e amplilicr 29 cornpii'ises a 2l) nrc. burst as indicated at 32. and is applied to the multicrystal array 17-21 via line 23.

A 20 incgacyclc continuons wave (indicated at 33) is also supplied by the oscillator' 27. via line 34, to the input of tlic` 2H megacycle narrow-band video amplifier 35. This amplifier (35) output then is supplied via line I6 to multicrystal array ll-lS which generates, along the plane of symmetry (i. a continuous ultrasonic waveform moving to the left (as viewed in FIGURE 2) and having an amplitude just below the cavitation level of thc liquid in the cell it. The excitation of multicrystal array l7-2l by sync pulse amplifier 29 generates, also along the plane of symmetry 6, an ultrasonic waveform of the same carrier frequency (2t) mc-) moving to the right and with peak amplitudes just below the cavitation level of the cell liquid. When the two opposing waveforms meet, their amplitudes are additive to produce a standing wave with an amplitude sullicient to cause hydrodynamic cavitation of the cell liquid. As a result of the induced cavitation, within ilte plane of symmetry 6. vertical lines of bubbles arc formed as shown at 36 in l`lGURE 2.

lt is not necessary to maintain tbe cavitation bubbles after formation` and they are allowed to collapse after every half-cycle of the ultrasound. Therefore, cavitation bubbles appear at any one instant of time only at the point where the ultrasonic hurst energy (viz. the energy l7-2l) happens to be. Since new btibbles arc being formed at every half cycle, the litres of bubbles appear to move along with the burst, and the formed buhlblc lines (eg. `36) continue to move on across the cell 4, within the plaire of symmetry 6, in the direction indicated by arrow 37. The envelope of burst wave sent to multicrystal array l7-2I is kept suflicicntly `short that upon meeting the opposite moving continuous wave from array ll'-IS, only a very few lines of cavitation bubbles are .formed at any one instant. The energy of each of the two colliding waves is balanced such that the restriting cavitation energy is maintained constant over thc operating length of the cell 4. Thusthc bubbles proditccd are always thc same size and qtiantity whether they are formed near the first array ll-lS or the second array l72l.

'lltic cavitation energy is maintained constant by interference focusing.

Thie bubbles (36) resulting from induced cavitation are formed and collapsed within one-half cycle of the imposed ultrasonic wave frequency. Since two vertical lines of bubbles of extremely' small diameter are formed,

they produce a diffraction grating elfcct on the light rays striking them in the cell at the plane of symmetry 6. As these vertical lines of bubbles move across the cell, the incoming lightJa-ys are difl'racted in a sweeping fashion upon interception as shown in FIGURE 2. The amount of light ditl'racted depends on the amount of light in the incoming bundle of rays 38 at that point, since the multicrystal arrays S11-15 and 17-21) are designed to maintain the lines of bubbles constant in number and amplitude as they move across the cell.

Since cell 4 will only scan a single line, in this case a horizontal line, of the image, vertical scanning is obtained by ancillary apparatus (eg. 3) as discussed hercinabove which will slowly move the image vertically across the centerline of the entrance window 7 of ccll 4 and may comprise a rotating mirror or a device of the type described in the above-mentioned copending application Serial No. 339.521.

As shown in FIGURE l, the dillractcd and undilfra-tcd rays leaving the cell are directed to a`schlieren optical system 39 which blocks out the undifl'racted rays, and

allows only the difiracted rays to pass on. As, is well known to those versed in the art, a Schlieren optical sys-i tem may be used to make visible, changes in optical parameters of a transparent material which produce anoinalous changes in the direction of propagation of a light ray. The Schlieren design used in this invention operates on the fact that the change in direction ofthe liglit rays in the plane of symmetry 6 are discrete changes` not gradual changes :is would be encountered in light passing through air of gradually changing density. The light rays passing through the platte of symmetry (i are citlicr undillractcd or dill'ractcd through a specific angle given approximately (for small angles) by:

d=1L/S where n is an integer representing the spectral order, AL is the wavelength of the light dilfractctl, and as is the spacing between thc lines of the diffraction grating (the lines of bubbles in this case. or one-half the wavelength ofthe ultrasound in thc liquid).

The optical system images the light source at some point after the light passes through the cell 4. The cell 4 is located at an aperture of this image, and the image of the light source is an aperture for the image of the plane of symmetry 6. Thus at the plane of the image of the light source, there will be a multiplicity of images, one for each spectral order of the dillracted light including the zero order (undiffractcd light). lt follows then that if an opaque material is located in this image plane so so to cover the image of the zero order spectrum. but not the other orders, then the undiffracted light will be eliminated while the dillracted light passes on and illuminates the screen. Refined sclilicren optical systems employing multiple slots or focusing are well known to those versed in the art. and the above brief description is considered sufficient for a complete understanding of the invention.

The ditfracted rays from the schlicren optical system 39 are focused by an auxiliary lens 4l onto the face of photomultiplier tube 42. lf the light rays 4passing through the lines of bubbles are a portion of an optical image created by the objective lens 2, thc bubbles will then sample a portion of this optical image. The amount of diffracted light entering the pliotoinultiplicr tube 42 is a function only of the amount of light received from the optical image at the location of the lines of bubbles in cell 4. Since bubbles exist only at the location of tlic 20 mcgacycle burst of ultrasonic energy, and the burst is traveling at the speed of sound in the liquid, the optical image is being scanned horizontally at this speed. The output from the photomultiplicr tubo 42. appearing on line 43, comprises a video signal derived from the line scan ofthe optical image, and is identical in form to video signals produced by conventional devices of the prior art. The video signal may be amplified by video amplifier t4 and transmitted to utilization equipment (not shown) via line 45. However, this video output signal has a considerably higher resolution and a lower noise level than the video signals derived from either a conventional vidi con or an image orthicon tube. The resolution, in terms of television lines, is given by the ratio ofthe length of' the cell to one-half of the spacing distance between the two bubble lines. The latter distance is a function of the frequency of the ultrasonic waveform within the cell. Thus. for a cell 1.5 inchcs long. with an ultrasonic excitation frequency ot' 50 uiegacyclcs, at a water temperature of 74 C.. the obtainable resolution is 2400 lines. This is greater than a three-told increase in optical resolution over thc best conventional vidicon. Increasing the length of the cell, arid/or raising the frequency of the ultrasound incrcases the horizontal resolution. The optical etlicicncy of the line scan device is a function of the diffraction angle in the cell; as this angle increases the optical cicicncy increases. This angle increases as thc ultrasonic frequency increases: therefore, at high ultrasonic frequencies. the line scan device not only has higher resolution. but higher optical efficiency.

inasmuch as each of the functional units represented by a block in the block diagram of FIGURE l may bc any one of the numerous devices foreach respective fitnetinn well known in the art, it is deemed unnecessary to show circuit details. Also. it should be understood that both the size of the bubbles and the spacing between the lines of bubbles. as shown in FIGURE 2, have been greatly exaA rated for illustrative purposes.

Since ecrtain chang-.cs may be made in tht` :ihovc dcsci'ihcd line scan device without departing front the scope of the invention herein involved. it is intended that all matter contained in the above description or shown in thc accompanying drawings shall be interpreted as illustrativc and not in a limiting sense. For example, the embodiment described may be modified to enhance the efliciency of tlic cavitation process.

lt is relatively diflicult to induce cavitation in pure degasscd water under conditions of high intensity sound. This is due primarily to the surface tension of the water which can sustain very large negative pressures in the body of the liquid. This internal cohesive force can be overcome by disbursing microscopic nuclei such :is polystyrene spheies ol' approximately O l micron diameter, throughout thc liquid. These nuclei must be smaller than a 'wavelength of light. otherwise` they themselves will scatter light and reduce thc optical efliciency of the device. The water within the cell may also be charged with a gasv such as carbon dioxide, which has a high vapor pressure at the operating temperature of the cell. This gas will diffuse into each bubble as it starts to grow from its nucleus, reinforcing its growth rate. Also a suitable agent may be added to the water to reduce its surface tension without wetting the polystyrene spheres (nuclei).

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the forni and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention; therefore. it is intended that the invention bc limited only as indicated by the scope of the following claims.

What is claimed is:

l. A line scan apparatus comprising:

means for projecting a line clement of an image along a given path:

a transparent liquid body located transversely of said path;

first means for continuously propagating acoustical en ergy into one end of said liquid body in a direction transverse to said path, said acoustical energy having an energy level helow that capable of producing cavitation in said liquid hotly; and

second mcans located t the opposite end ol' said liquid body for. cyclicall propagating bursts of acoustical cy therefrom, a `second input. and an output connected to said .second array of tran\ducers; and

a pulse generator connected to said secondginput of said moduh-.tor means to cyclically control thc ultraenergy transversely to said path and in the opposite 5 sonic frequencyl at said output and thus cause said direction to said continuously propagated acoustical second array to he eyclically excited at an ultrasonic energy, the summation of said continuously profrequency. pagated and said cyclically propagated energy from 7. Radiant energy scanning apparatus comprising: said first and second means, respectively, producing optical means for focusing image rays emanating from cavitation within said hody at their meeting points IOL aradiant source alonga line dement; when the summation of said energies equals or exa confined holly of liquid, transparent to said image ceeds that required for cavitation. the cavitation prorays comprising said line clement over a continuous ducing a localized diflraction grating in said body portion thereof; which sweeps transversely aci-Ogg Said path, first transducer means located at one end of said eon- 2. A line scan apparatus as defined in claim 1 wherein 15 tintious portion for continuously propagating ultrasaid first acoustical energy propagating means comprises: sonic energy along the length of said continuous pora first array of piezoelectric transducers arranged to tion. said level of ultrasonic energy being heloiv the concentrate the acoustical energy output therefrom level required to induce cavitation in said liquid; in aplanetransverse to said path. second transducer means located at the opposite end 3. A line scan apparatus as defined in claim l wherein 20 0f Sld Continuous holly Portion for CYCICIIHY Pmsad second acoustical energy propagating means com- Ulltlllng n Wm 0f UUFISOUC CnCV-Y m10 Sad liquid prises: in a direction towards said first transducer means;

a second array of piezoelectric transducers arranged ntl to concentrate the acoustical energy output there- PIUUCCCVC mt-lm ffPOnVC l0 mI'LUC fnl/S Pfl-Sing from in a plum tmmvcrsc 10mm path, 25 through said continuous portion, the level of the 4. A line scan device as defined in claim 1 wherein UllriiOnC CnCVlY Dl'OPiltlnlCd by Sld first and SCC- said liquid body comprises water to which has been added 0nd lmlsdlccr mcns bein? ndllllllf'c 'l'lhn Sld littan agent to reduce surface tension and dispersed solid Uld body Fl the 'million-0f the mclnfl POU 0f lllC nuclei having diameters of the order of 0.l micron. to 1WD CHCYSY Wlf'C fVO'US l0 PYOUCC CUVUUOH lhCl'En promote cavitation. 30

S. A line scan apparatus as defined in claim 2 having: ICCTMCS 't cd h5' uw Exil'm'm' oscillator means connected to said first array of trans UNlTl) STATES PATENTS duccrs for continuous excitation at an ultrasonic 943315 6/,960 Rmcmhn] 88 61 frequency. 6. A line scan apparatus as defined in claim 5 having: 35 DAVtD G. REDINBAUGH Primm), EMM-0n modulator means having a first input connected to said oscillator means for receiving an ultrasonic t'requcn- J A' ORSINO 1MM/"Hl E'w'mim Disclaimer an Mat-ino, Calif. LINE SCAN DIC- VICE UTILZING CVITATJION PHENOMIA PRODUCED IN AN ULTRASONIC CELL. Patent. dated Feb. 28, 1967. 1,)15- claimer filed June 2, 1967, by the assignee, The All arg1/ardt Corporafzon.

Hereby enters this disclaimer to claims l through 6 of said patent.

[Oficial Gazette August $2.9, 1967.] 

1. A LINE SCAN APPARATUS COMPRISING: MEANS FOR PROJECTING A LINE ELEMENT OF AN IMAGE ALONG A GIVEN PATH; A TRANSPARENT LIQUID BODY LOCATED TRANSVERSELY OF SAID PATH; FIRST MEANS FOR CONTINUOUSLY PROPAGATING ACOUSTICAL ENERGY INTO ONE END OF SAID LIQUID BODY IN A DIRECTION TRANSVERSE TO SAID PATH, SAID ACOUSTICAL ENERGY HAVING AN ENERGY LEVEL BELOW THAT CAPABLE OF PRODUCING CAVITATION IN SAID LIQUID BODY; AND SECOND MEANS LOCATED AT THE OPPOSITE END OF SAID LIQUID BODY FOR CYCLICALLY PROPAGATING BURSTS OF ACOUSTICAL ENERGY TRANSVERSELY TO SAID PATH AND IN THE OPPOSITE DIRECTION TO SAID CONTINUOUSLY PROPAGATED ACOUSTICAL ENERGY, THE SUMMATION OF SAID CONTINUOUSLY PROPAGATED AND SAID CYCLICALLY PROPAGATED ENERGY FROM 